Surface treatment for zinc base alloys



' Patented July 24, 1934 UNITED STATES PATENT OFFICE SURFACE TREATMENT FOR ZINC BASE ALLOYS No Drawing. Application June 2, 1933, Serial No. 674,035

3 Claims. (Cl- 148-8) This invention relates to means and methods of forming corrosion resisting coatings for zinc base alloys and particularly to such alloys as are ordinarily used for die casting purposes.

5 Attempts have previously been made to coat such alloys with black nickel, phosphates and copper, but these methods. were not entirely satisfactory because they did not completely protect the surface nor did they sufilcientl'y resist the corresion. In addition to this certain of these treatments produce an unsightly coloring on the surface of the zinc which was, of course, objectionable.

It is an object of this invention to produce a is corrosion resisting coating for zinc base alloys which will be of sufficient density to protect the alloy from the action of moist atmosphere, salt spray and the like.

It is a further object of this invention to produce a corrosion resisting coating for zinc base alloys which will be. sufliciently dense to protect the material from corrosion and yet not so thick as to substantially change the dimensions of the casting or to fill up any small cast passageways which may have been formed therein. I

It is a further object of this invention to produce a corrosion resisting coating for zinc base alloys of such a nature that the coated casting will have substantially the same appearance as the original uncoated casting; or in other words to produce a substantially invisible or nonnoticeable corrosion resisting coating for such alloys.

This invention is applicable generally to zinc base alloys some of which are listed below for purposes of illustration:

may be made as follows:

4 oz .Nickel chloride 6 oz. .Zinc chloride y, oz Ammnnium chloride 5 2 oz Ammnninm tmocymte oz "Potassium dlchromate 1 gal.. .Water The above solution is heated to the boiling point or slightly below and the castings to be treated are immersed in the bath for a period of approximately five minutes, and then removed and dried. It will be understood, or course, that all grease, oil and dirt must be removed from the castings prior to the treatment. The cleaning may be done by any of the well known methods for cleaning such material such as immersion in a sodium hydroxide bath or washing with carbon tetrachloride, oakite, or xylene.

Castings of zinc base alloys when treated by the method above described have strong corrosion resisting qualities and also a neat appearance and there is no chance of clogging up any small passageways which may be formed in the casting.

The exact chemical reactions that take place in this solution are not fully understood at this time except that chromium in some form is deposited on the surface of the casting in a thin 'but strongly adhesive layer. It is quite possible that there is also some deposition of nickel. However, it is fully established that zinc base alloys may be given a very satisfactory protective coating by the practice of the above described method.

Iclaim:

1. The method of coating zinc base metals which comprises immersing them in a solution v containing zinc chloride, ammonium chloride, ammonium thiocyanate, and an oxygen contain- 1 ing chromium salt of an akali metal.

2. The method of coating zinc base alloys which comprises immersing them in a solution containing nickel chloride, zinc chloride, ammonium chloride, ammonium thiocyanate, and a salt from the group consisting of alkali metal chromates and dichromates.

3. The method of providing zinc base alloys. with a corrosion resisting coating which comprises immersing them in a solution containing zinc chloride, ammonium chloride; ammonium thiocyanate and a salt from the group consisting of alkali metal chromates and dichromates.

WILLETT C. MAGRUDER, Jr. 

